1. Field of the Invention
The invention relates to a substrate and, more particularly, to a substrate that is applied to an optical disk.
2. Description of the Related Art
An optical disk can store data in different formats, such as image data, digital image data files, and text files; therefore, an optical disk is the most convenient storage medium among the new generation optical storage media. In addition, the scope of fields that an optical disk can be applied to is very broad, including library archives, data backup, electronic publication, image data storage, and personal medical record management.
The structure of a conventional optical disk substrate 500 is shown in FIG. 5(a), which shows a side view of a conventional optical disk substrate. Herein, a DVD-R optical disk, which is a type of DVD optical disks, is taken as an example and shown in FIG. 5(a). The optical disk substrate 500 has a transparent base plate 501 capable of stacking a recording layer 502, a reflection layer 503, and a protection layer 504, in this order, over the transparent base plate 501 in sequence. On the other hand, FIG. 5(b) is a top view of a conventional optical disk substrate 500. As shown in FIG. 5(b), a clamping area 506 used for clamping is provided around the outer edge of a central hole 505, and an annular information storing area 507 is provided around the outer edge of the clamping area 506. In addition, the diameter of the optical disk substrate 500 is 120 mm, the diameter of the central hole is about 15 mm, and the outer diameter of the clamping area is about 15.5˜48 mm.
Also, referring to FIG. 6, which is a side view of a conventional optical disk 50, the specified thickness of the optical disk substrate 500 is 0.6 mm. Additionally, the optical disk 50 normally also includes a compensation sheet 600, whose dimension is the same as that of the optical disk substrate 500, namely 120 mm. Besides, a central hole is also provided thereon with a diameter of 15 mm. Since the thickness of the compensation sheet 600 is 0.6 mm, adding this thickness to that of the optical disk substrate 500 makes a finished optical disk 1.2 mm in thickness. Therefore, the strength of the optical disk can be enhanced so that when the optical disk is revolving in the optical disk drive, the optical disk will not be distorted due to high-speed revolution and thus may avoid a reading problem on the disk drive.
Next, FIG. 7 is a schematic view of an optical disk being placed in an optical disk drive. As shown in FIG. 7, when a disk drive is reading from an optical disk 50, the disk drive of the drive device utilizes a disk chuck 701 to clamp on the clamping area 506 of the optical disk 50. Therefore, the optical disk 50 will be clamped between the disk chuck 701 and the disk turntable 702 and driven by a disk turntable driving motor (not shown) to revolve together with the disk chuck 701 and the disk turntable 702. Moreover, the distance (d) between the laser reading head 703 and the optical disk substrate 500 will be kept unchanged so that the laser of the optical disk drive can be reflected back by the reflection layer 503 of the optical disk substrate 500 and thus information in the optical disk 50 can be read out.
However, during the process of fabricating the optical disk, an extra step will be required for pressing or bonding the compensation sheet 600 to the optical disk substrate 500. Unfortunately, not only will this extra step reduce the yield of optical disk substrate, but the quality of optical disk can also decline. Moreover, in order to fabricate the compensation sheet 600, extra injection molding apparatuses might be needed, and this extra requirement will certainly increase time and cost for fabrication tremendously.